3S ESC
- Kenny Na
Description
BLDC motor controller compatible with 3S systems. Will initially be standalone, connecting to 12V -> 5V @ 4A Buck Converter + ELRS Board externally and then later physically integrated into another board revision for an all-in-one fixed wing solution.
Depending on the cost and performance of the board, it may be integrated elsewhere. Target design parameters are also being pulled from Houston spec in Houston: Configuration.
Electrical Designer: @Kenny Na (WARG EE F24 Co-op)
Project Manager: @Daniel Puratich
Requirements
Powered by a 3S (12V) battery input.
In the context of integrating with the ELRS board, an XT60 connector should be provided, and additional input from a header pin should be placed for speed control.
3x solder pads for BLDC connection.
Supports DSHOT input.
More resistant to noise in transmission versus PWM, as DSHOT is a digital protocol.
12-5V Buck + ELRS was designed with PWM in mind but this can be altered.
An “OPTO” ESC, meaning no BEC is included.
Must use the AM32 open-source firmware for motor control. (https://am32.ca)
This uses a sinusoidal algorithm to control the BLDC. (no FOC)
Has a strict MCU compatibility list (we would preferably use a smaller ST chip)
Operation using back EMF and possibly current sensing. Likely no Hall sensing.
Designed around an target motor (in Houston): https://innov8tivedesigns.com/cobra-cm-2217-20-brushless-motor-kv-950.html
Standard 3-phase brushless DC motor with 12 stator windings and 14 exterior magnet poles, meaning 4 coil windings per phase. Designed for 3S/4S power source.
With a higher density of magnet poles in the rotor, smoother torque is able to be produced by the motor. The rotor being on the outside gives more torque as well.
Maximum continuous current of 20 Amps.
Maybe 25A or 30A maximum burst current.
Should be accounted for during FET selection.
Components
Microcontroller Selection
Compatibility with AM32
AM32 provides a list of supported microcontrollers in their GitHub repository’s README file. Additionally, there is an MCU “target compatibility list” that can be found inside of the code. These were used to guide the selection of an appropriate MCU.
Comparison Table
Microcontroller | Option 1 | Option 2 | Option 3 |
|---|---|---|---|
Name | STSPIN32F0 | STM32L431 | STM32F051 |
Price/unit | $4.34 | $5.20 | $5.59 |
Notes | Integrated MCU with STM32F031, DC-DC, LDO, and gate driver for BLDC applications. Capable of FOC, 6-step, Hall sense, etc. Price can’t really be compared to other options. Physical size of ESC would be more compact since gate driver is integrated. | Existing design part of WARG, cheaper option. | Used in previous ESC design from WARG, may possibly be overkill. |
FET Selection
Main things to keep in consideration are the 20A max continuous current requirement, and any peak/transient current draw requirements from the motor. The STSPIN32F0’s gate driver can do 600mA sink/source.